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Combat Robots Wiki

Battery safety & charging

LiPo packs are the main workshop hazard in insect-class combat robotics. A damaged or abused cell can vent flammable gas and ignite.

Charging

Section titled “Charging”
  • Use a balance charger and always plug in the balance lead.
  • Set the right chemistry. LiPo and LiHV are different modes. Charging a LiPo on the LiHV setting overcharges it — a fire risk; charging a LiHV on the LiPo setting just stops it short of full.1
  • Charge at 1C (capacity in amps — an 850 mAh pack → 0.85 A). Higher is possible in a pinch but shortens pack life; stay at 1–2C.21
  • Charge in a fireproof container (LiPo bag, ammo can, ceramic pot) on a non-flammable surface, never unattended, never overnight.
  • Stop if a pack gets hot, puffs, or a cell reads oddly during balancing.
  • Full charge is 4.20 V/cell for LiPo, 4.35 V/cell for LiHV. Never exceed it.

Storage

Section titled “Storage”
  • Store at ~3.8 V/cell (“storage voltage”). Most chargers have a storage mode. Don’t leave packs plugged into the robot or charger.1
  • Don’t leave packs full for more than a day or two.
  • Don’t discharge a cell below 3.3 V in use; below ~3.0 V it likely has damage, and below ~2.6 V dispose of the pack.1
  • Measure each cell at the balance lead, not just the pack total — one cell can collapse while the others look fine.
  • Cool, dry, in a fire-safe container.

Physical protection in the robot

Section titled “Physical protection in the robot”
  • Mount the pack where weapon impacts and internal debris can’t reach it — behind structure, not against thin armor.
  • No hard points pressing into the pack; no fasteners that can puncture it under shock.
  • Secure it so it can’t come loose in a big hit (strap, tray, hook-and-loop plus a positive retainer).
  • Route the discharge leads so they can’t be cut or pinched.

Damaged packs

Section titled “Damaged packs”
  • A pack that took a hit, was pierced, or puffed is done — do not charge it.
  • Discharge a suspect pack slowly (a small resistive load over days, or a salt-water bath over weeks), then dispose of it at a battery recycler. Never the household trash.1
  • Have a way to move a venting pack outside — this is what the LiPo bag is for. Lithium fires can’t be put out by normal means; get the pack out and let it burn. The white smoke is dense and toxic; don’t breathe it.1

Events require sane battery practice and will fail robots with exposed or damaged packs at tech inspection.3

References

Section titled “References”

Footnotes

Section titled “Footnotes”

  1. Ping, L., with L. Skotiniotis, I. Talbert & D. Tran. Beetleweights for Dummies (Fall 2025 revision) — builder-maintained beginner guide distributed via the NHRL Discord. Section: Testing & Safety → LiPo Battery Safety. ↩ ↩2 ↩3 ↩4 ↩5 ↩6

  2. Battery University (Cadex), BU-808: How to Prolong Lithium-Based Batteries — charge rate, full-charge and storage voltages, and failure modes. ↩

  3. SPARC Robot Construction Specifications, v1.4, 2023 — battery mounting, protection, and inspection requirements. ↩